He threw away tax documents, got a ticket for trying to pass an ambulance and bought stock in companies that were obviously in trouble. Once a good cook, he burned every pot in the house. He became withdrawn and silent, and no longer spoke to his wife over dinner. That same failure to communicate got him fired from his job at a consulting firm.

By 2006, Michael French — a smart, good-natured, hardworking man — had become someone his wife, Ruth, felt she hardly knew. Infuriated, she considered divorce.

But in 2007, she found out what was wrong.

“I cried,” Mrs. French said. “I can’t tell you how much I cried, and how much I apologized to him for every perceived wrong or misunderstanding.”

Mr. French, now 71, has frontotemporal dementia — a little-known, poorly understood and frequently misdiagnosed group of brain diseases that eat away at personality and language. Although it was first recognized more than 100 years ago, there is still no cure or treatment, and patients survive an average of only eight years after the diagnosis.

But recently, researchers have been making important discoveries about the biochemical and genetic defects that cause some forms of the disease. And for the first time, they have identified drugs that may be able to treat one of those defects, the buildup of abnormal proteins in the brain. Tests in people, the first ever such drug trials in this disease, could begin as soon as early next year at the University of California, San Francisco.

“There’s really been an explosion related to the biology,” said Dr. Bruce L. Miller, a professor of neurology and psychiatry there. “I think at least some subtypes of frontotemporal dementia will be the first neurodegenerative diseases we find a cure for.”

This disease is different from Alzheimer’s, the most common form of dementia. But it is perhaps even more devastating, because it strikes younger people, progresses faster and, unlike Alzheimer’s, does not attack memory at first but begins with silence, apathy or bizarre personality changes. It is thought to afflict at least 50,000 to 60,000 people in the United States.

The scientific findings in frontotemporal dementia may also reshape thinking about the fundamental flaws involved in Alzheimer’s disease.

“I think the way dementia is going in general now is to realize there are many different subtypes,” Dr. Miller said, adding that what is now labeled Alzheimer’s disease may actually turn out to include hundreds of different illnesses.

Dementia is a formidable adversary, and the history of efforts to treat Alzheimer’s has to temper any excitement about potential medicines for frontotemporal disease. The drugs for Alzheimer’s have been a disappointment, with just temporary effects on symptoms at best.

But even if treatments or cures for frontotemporal dementia do emerge, they will almost certainly come too late for people with advanced cases, like Mr. French or Richard Rainwater, a billionaire investor who learned in 2009 that he had progressive supranuclear palsy, which some consider a form of frontotemporal dementia. Mr. Rainwater and his family have donated more than $20 million to a research consortium, but given that he has a rapidly progressive form, any advances from the consortium may be more likely to help others than to save him.

Looking for Answers

Looking back, Mrs. French, who is 66 and lives in Manhattan, recalled episodes of odd behavior over the years and realized that her husband’s mind had probably begun to slip while he was in his 50s, at least a decade before the disease was diagnosed. He had always changed jobs a lot. At the time she took it as a sign of a stubborn personality, not of illness — and it is still not clear which it was. He always wanted to do things his own way, and that did not sit well with some bosses.

“I thought it was just Michael being Michael,” she said.

A friend described Mr. French as being unable to read the tea leaves, oblivious of corporate politics. At one point Mrs. French even bought him a self-help book. But he never changed.

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Mrs. French with her husband, whose frontotemporal dementia was diagnosed in 2007 by a neurologist after he began to have trouble speaking.Credit
Béatrice de Géa for The New York Times

And he always found another job, better than the one before. But things went downhill in 2006.

“His immediate boss was so frustrated by him that she called up, and we were at the dinner table, and I could hear her screaming,” Mrs. French said.

He was fired, and this time he did not find another job. At 66, he retired.

Soon after, because he had trouble speaking, he consulted a neurologist. When they got the diagnosis, Mrs. French asked the doctor, “How do we treat it?”

“It’s brain atrophy,” he replied.

Her thoughts of divorce evaporated. Instead, she told her husband: “Whatever happens, we will go through this together. I will be there.”

From then on, the silence at the dinner table no longer troubled her. It did not seem personal anymore. He was not refusing to talk; he simply could not. Her anger melted into sadness.

But sometimes she still blew her top. Once, she came home and found him at the stove, seemingly unaware that his oven mitt was smoldering.

“I actually hit him a couple times out of frustration,” she said. What made her lose control, she said, was a toxic mix of frustration and fear — fear of what was happening to him, and fear that she would not know what to do, how to help. No amount of information from his doctors could put her at ease.

“They can tell you everything that’s ever happened to anyone, but they can’t tell you what’s going to happen to you,” she said.

The last five years have been wrenching and often lonely. Michael was the love of her life. When she married him, her sister asked, “How does it feel to hit the jackpot?” In more than 30 years of marriage, she never heard him say an unkind word about anyone. He was an engineer, lectured at conventions, did volunteer work, belonged to a history book club, ran marathons. Now he can no longer speak, read, write or walk.

If there is comfort anywhere for Mrs. French, it is in knowing one thing: she has kept her promise to be there.

The Science

Frontotemporal dementia, also called frontotemporal degeneration or Pick’s disease, refers to a group of diseases that destroy nerve centers in the frontal and temporal lobes — the home of decision-making, emotion, judgment, behavior and language. Some forms of the disease also cause movement disorders.

Most cases occur sporadically, in people with no family history of the illness — like Michael French — but a small percentage are inherited.

Patients generally receive from one to four misdiagnoses, and it may take years to finally get the right answer. Mistaken diagnoses can include Alzheimer’s disease, stroke, midlife crisis or psychiatric illnesses like depression, bipolar disorder, post-traumatic stress or anxiety. Many relatives of patients say doctors dismiss their reports of personality change. But it is real.

“They totally break down in their ability to connect with other people and care about them,” Dr. Miller said.

There are eight subtypes of frontotemporal degeneration, sorted by the symptoms they cause. Some affect behavior. Others, grouped under the heading primary progressive aphasia, affect language. Still others affect movement, leading to disorders that resemble Parkinson’s or Lou Gehrig’s disease (also called amyotrophic lateral sclerosis or A.L.S.).

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Looking back, Mrs. French thinks her husband's mind began to slip a decade earlier.Credit
Béatrice de Géa for The New York Times

But patients may match more than one category, and the subtype may change as the disease progresses.

“I see a lot who don’t present like the textbook,” said Dr. Edward Huey, an assistant professor of psychiatry and neurology at Columbia University Medical Center.

In most patients, MRI and other scans reveal shrinkage in the frontal and temporal lobes, sometimes to a shocking degree.

“If I showed you more extreme cases, you could read it from across the room,” Dr. Huey said.

He said researchers were using imaging to find out if specific symptoms could be mapped to atrophy in certain spots.

“The frontal lobes are sort of the last frontier in the brain,” Dr. Huey said, adding that the losses these patients suffer are helping researchers understand more about what the frontal lobes do. As the brain atrophy progresses, Dr. Huey said, patients “have pieces of psychiatric syndromes, but not the whole syndrome.” For instance, they have compulsions, but not the usual accompaniment, obsessions. So they may wash their hands over and over again, but not in a worried or anxious way. Some lose their inhibitions and moral judgment. Shoplifting is not uncommon. Many have the apathy and social disconnection that usually go with depression, but they do not feel depressed.

“They’re not down, but they just don’t enjoy things as much as they used to,” Dr. Huey said. “There appears to be a dysfunction in the reward circuit, where activities that were rewarding and pleasurable no longer seem to be. These patients lose themselves.”

Many seem to go on endless eating binges and gain weight. It is not clear why — whether they are actually hungry or whether the eating is just another compulsion. Some people with the illness shower repeatedly or check the mail 100 times a day. One possible reason, Dr. Huey said, is that “the part of the brain that tells you, ‘No, that task is done,’ is gone.” Some patients collect things — by the hundreds. A few have had bursts of creativity in music or painting, possibly because other brain regions come to the fore as the frontal lobes wither.

A Way of Life Cut Short

Long before her husband became ill, Mrs. French had a successful career in sales and marketing for textile companies and ultimately became a vice president at Liberty of London. But she gave it up in 1991 to do something she loved: teaching English as a second language to adults. She was doing that work when his condition was diagnosed.

One day, in a moment of inspiration, she asked her students if they knew the traditional wedding vows in English. She began to recite them. At “for better, for worse,” she choked up. Struggling to keep her composure, she quickly finished and moved on to another subject.

After teaching, she would walk home through Central Park, and in the early days of his illness Mr. French would often meet her halfway. She would see him heading toward her, smiling and strikingly handsome. “When I look at Michael, that’s what I see, that’s who he will always be to me.”

In 2007, Mrs. French joined a support group for caregivers of people with frontotemporal dementia. Jill Goldman, a genetic counselor at Columbia University Medical Center, said she started the group because patients’ relatives felt that they did not fit in at Alzheimer’s groups; their loved ones were younger and often had bizarre behaviors that were nothing like Alzheimer’s.

“One of the things that goes first is insight,” Ms. Goldman said. “ ‘There’s nothing wrong with me. Why can’t I do what I want to do?’ ”

Members of the group tell of loved ones who hug strangers, who fly into terrifying rages and hit family members and health aides, or who pass their days in silence cutting up newspapers or watching television. Patients are easily taken in by financial scams that can cost families thousands of dollars. Often, apathy sets in, and people once devoted to their families lose interest in everyone, even their own children.

“My son and I look out the window and see my wife out there, stepping on leaves, and we start to cry,” one member said.

Some have struggled with uncertain diagnoses because patients have symptoms of both Alzheimer’s and frontotemporal disease. One wife described trips to multiple doctors and inconclusive reports on PET scans and spinal taps. Should she have taken her husband to the Mayo Clinic? She agonized over the idea that he might have some illness other than frontotemporal dementia or Alzheimer’s, something treatable, and that there might be some way to rescue him, to bring him back.

Photo

Mr. French was an engineer, lectured at conventions, belonged to a book club and ran marathons. Now he can no longer speak, read, write or walk.Credit
Béatrice de Géa for The New York Times

Another said her husband, a judge who had always been mild-mannered and modest, turned boastful and began talking to strangers in the street, making jokes at the wrong time and falling for scams.

“He salutes every flag, closes every gate, kisses every hand,” she said.

Riding the bus in Manhattan, he will loudly announce, “I haven’t killed anybody lately.” Not infrequently it gets him a seat. He can turn violent and has struck a health aide with his cane.

“He’s just mean and nasty,” his wife said. “He was such a wonderful man. He’s not a person anymore.”

Ms. Goldman provides stacks of business-size cards that spouses can hand out to strangers in awkward situations.

“My husband has a terminal brain disease called frontotemporal dementia,” the cards read. “Thank you for your understanding.”

Many find that friends and family pull away. Nearly all grapple with whether and when to take away car keys, give drugs to blunt aggression, hire a health aide or put the patient in a nursing home. One group member said, “The doctor told me, ‘You’re taking good care of him, he’ll live a long time,’ and I said, ‘Why is that a good thing?’ ”

Patients are hard to care for at home, and those who are young, strong and aggressive are sometimes kicked out of nursing homes because they are seen as posing a physical threat. But employers do not necessarily sympathize with relatives called out of work in the middle of the day because a patient has punched or shoved someone at the nursing home.

“My boss says, ‘You just have to deal with this better,’ ” one group member said.

Another group member, a professor of psychotherapy and mental health counseling, said she quit her job at the height of her career to take care of her partner and after a few years became suicidal.

“Being a caregiver in this disease is a grieving process,” she said, “while the person is still alive.”

Easing the Burden

Ruth and Michael French managed on their own until May 2009, when he fell down a flight of stairs in their apartment building while she was at work. He fractured his skull and came home in a wheelchair, so weak and frail that she hired an aide to help take care of him.

Mrs. French is fine-boned and thin, and as her husband grew weaker, the physical demands on her became daunting. Streets she had thought flat revealed themselves to be hills once she found herself trying to push a 140-pound man in a wheelchair. Potholes yawned like chasms. One night at home, after helping him clean his teeth, she turned to put the toothbrush away, and in that moment he fell into the bathtub. She was barely able to pull him up.

“I said, ‘Michael, now we’re at the point where we’re both at risk,’ ” she recalled.

She injured her wrist, developed a stomach ulcer and lost so much weight that people worried about her. Mr. French became incontinent, and she would sometimes wake up in a pool of his urine. The health aide hurt her back lifting him.

“I heard myself say one day, ‘I would never want anybody to do for me what I’m doing for Michael,’ ” Mrs. French said.

She had hoped to keep him at home until the end but knew it might not be possible. “This thing is going to kill both of us, and I don’t know who’s going first,” she told him.

Photo

On most days, Mrs. French spends several hours with her husband at the nursing home in Manhattan where he now lives. She had to move him there last year after she was no longer physically able to take care of him. “At times, I ache for him to be back in the apartment,” she said. “But I ache for him to be back as him.”Credit
Béatrice de Géa for The New York Times

In one way, she had an easier time than many other caregivers. Her husband never turned hostile. He retained a sweetness, and an acceptance of his illness that she found inspiring.

At one point, worried about finances, she considered laying off the aide and taking care of Michael alone. When members of her support group worried that the stress would kill her, she told them, “That might not be so bad.”

At Ms. Goldman’s urging, she saw a psychotherapist. He recommended medications to calm her. She filled the prescription but threw the pills away.

“I kind of feel that having gone through the anxiety and the worry is what let me get to the other side,” Mrs. French said.

While Mr. French was still well enough, they had discussed the possibility of a nursing home. So when the time came, it was not really a surprise.

“He knew it was something I didn’t want to do, because every time we spoke about it I would cry,” Mrs. French said. “When I told him that I had made arrangements, he said — and this is a man who can’t speak, so he had to muster every bit of energy he could — he said, ‘You did the best you could.’ ”

In April last year, Mrs. French placed her husband in a nursing home in Manhattan. Along with her sadness came feelings of relief and freedom. Soon after he was settled, she went out to dinner with friends for the first time in two years.

“At times, I ache for him to be back in the apartment,” she said. “But I ache for him to be back as him.”

She said that long after he ceased speaking, he continues to understand what she says.

“I remember asking his neurologist, ‘Will he know me?’ ” Mrs. French said. “And he said, ‘Oh, he’ll always know you. He might not be able to express it in a way that will be familiar to you or that you’ll like, but he’ll always know you.’ ”

She wondered what longings might drive her husband’s dreams:

“I asked him, ‘Do you talk in your dreams?’ and he said, ‘Yes.’ And I asked him, ‘Do you dream about me?’ And he said, ‘Yes.’ ”

She has had time to think about mortality, his and her own.

“Death to me has always been a wake-up call to live,” she said. “This is the endgame. Sometimes I get upset because I don’t think I have enough money, and sometimes I get upset because I think I do. You don’t necessarily want to live too long, but neither do you want to die.”

On most days, she spends several hours at the nursing home with her husband. She shaves him and sometimes climbs into bed with him to hold him and to nap together.

“Where do you carry my heart?” she asks him, referring to a poem they love by E. E. Cummings.

He smiles and pats his chest.

i carry your heart with me(i carry it in

my heart)i am never without it(anywhere

i go you go,my dear;and whatever is done

by only me is your doing,my darling)

i fear no fate(for you are my fate,my sweet)i want

no world(for beautiful you are my world,my true)

Excerpt reprinted from “Complete Poems: 1904-1962” by E. E. Cummings, ed. George J. Firmage. With the permission of the Liveright Publishing Corporation.

A version of this article appears in print on May 6, 2012, on page A1 of the New York edition with the headline: When Illness Makes a Spouse a Stranger. Order Reprints|Today's Paper|Subscribe